The present disclosure relates generally to construction of marine risers.
In offshore drilling, a marine riser is used to connect a floating rig to a seafloor. The marine riser provides a conduit through which fluid and equipment can be passed between the rig and a well drilled beneath the seafloor. The lower end of the marine riser is normally flexibly latched to a blowout preventer stack at the seafloor, whereby the marine riser is permitted to deflect angularly as the floating rig sways or drifts. The upper end of the marine riser normally includes a telescopic joint connected to the floating rig to compensate for heave of the floating rig. A system of riser tensioners located on the floating rig applies tension to the upper end of the marine riser so that the marine riser does not buckle under its own weight.
A marine riser of a desired length is made by connecting several marine riser segments together. Each riser segment includes a central pipe with a length of, for example, about 75 ft. (22.86 m). Each riser segment may also include auxiliary conduits external to the central pipe. The auxiliary conduits may include a mud boost line, choke and kill lines, and hydraulic conduits, e.g., for functions such as glycol injection, hydraulics, riser fill-up, and so on. Each pipe or conduit included in the riser segment represents a pipe connection that may be made when several riser segments are connected together to form the marine riser. Therefore, the ability to quickly make up connections between riser segments continues to be an important aspect of designing marine risers, especially as drilling moves into deeper waters, which may require that more riser segments are joined together to form the desired marine riser length.
When marine riser segments are assembled end to end, the central pipes form a main conduit. In conventional marine risers, the main conduit may be required to carry much of the tension load in the marine riser. This means that the main conduit would have to be designed to withstand the maximum expected tension load while the marine riser is in use. This tension requirement may increase as the depth of water between the floating rig and the seafloor increases. An approach when confronted with meeting higher tension requirement may be to increase the diameter and wall thickness of the central pipes. While this may yield a stronger main conduit, the marine riser also becomes heavier, which would result in greater burden on the system of riser tensioners. In many cases, adjusting the geometry of the central pipes also means that the connector geometry between riser segments has to be redesigned.
U.S. Pat. No. 6,419,277 (“Reynolds”) discloses a marine riser including a plurality of riser joints connected to each other by threaded connections. Each riser joint has a threaded coupling at each end. Flanges are coupled to the riser joint by bearings, which can be ball, roller, or any other type that will enable relative rotation between the joint and the flanges. The flanges have openings for auxiliary conduits, e.g., mud boost line, choke/kill line, and hydraulic conduits. Because the flanges are coupled to the joint through the bearings, when the joint is assembled to a corresponding joint, the joint can be rotated while the flanges and the auxiliary conduits can remain rotationally fixed. This enables the joint to be connectible to other such joints using conventional threaded coupling methods. Reynolds discloses that the auxiliary conduits may be joined together using any type of connectors known in the art and specifically suggests slip-type connectors disclosed in U.S. Pat. No. 4,496,173 (“Roche et al.”).